In many electricity grids, a considerable portion of the power is already being generated by wind energy installations. Besides the advantage of regenerative energy generation and decentralized supply of active power, they afford the advantage that in order to support the grid in the event of a fault, reactive power can also be provided in a decentralized manner by modern wind energy installations. It is thus possible to react effectively to balanced grid faults. However, difficulties can occur in the event of unbalanced grid faults. Oscillations can then occur in the drivetrain of the wind energy installation. Such oscillations load the rotor-generator system and increase the risk of failure of a wind energy installation.
It has been proposed to counteract torque oscillations caused by unbalanced grid faults by means of a so-called negative phase sequence system regulation mechanism. Such a mechanism has been described in an article “Transient Performance of Voltage Source Converter under Unbalanced Voltage Dips” by Magueed, F. et al. A negative phase sequence system is formed in concurrently rotating d, q coordinates, such that it becomes a DC signal. Current unbalances occurring in the generator can be compensated for by addition and inverse transformation. The torque oscillations are thereby reduced. However, that is confronted by a disadvantage, namely that larger voltage unbalances occur in return. In this respect, the grid is therefore loaded with additional unbalance.
Although it is known that synchronous generators can be provided in the grid in order to provide a remedy, this gives rise to additional outlay.